implemented delay

[tomoyanonymous]

Implemented delay.

In this implementation, user need to specify maximum delay size as a first argument, and the argument need to be a number literal to evaluate at compilation time.
In the future spec, some constant folding using multi-stage computation will be introduced.
For example, delay with feedback can be written like this.

fn fbdelay(input,time,fb,mix){
    input*mix + (1.0-mix) * delay(40001.0,(input+self*fb),time)
}